In metal production furnaces, such as electric arc furnaces, the furnace vessel has a hearth made from refractory materials at its bottom. The furnace walls surrounding the hearth may also be made from refractory materials, or they may be made from water cooled metal panels. Smelting material is placed in the furnace and melted. In electric arc furnaces, electrodes are lowered into the furnace into proximity with the smelting material, and the resulting electric arcs melt the material in the furnace. The refractory construction of the furnace hearth allows the hearth to withstand the temperatures required to melt the smelting materials. The resulting melt frequently comprises a layer of melted metal at the bottom covered by a layer of slag. The slag layer comprises the other, undesirable, constituents of metal ore or metal scrap melted in the furnace.
To control the content of the material in the furnace melt, other, additional material is added into the furnace environment. For example, the carbon content of iron melts is controlled to determine the type of steel produced. The additional material is added with gas jets directed into the melt. In some cases, particulate ingredients may be added. In situations in which it is desired to adjust the carbon content, oxygen jets are directed into the melt to form carbon dioxide and extract carbon from the melt. The jets are delivered with oxygen lances placed in the lower portion of furnace. The furnace walls have portals or holes left open in the walls down near the hearth, and injection lance shields, seat into these portals. The shields, more or less close the portal between the interior and exterior of the furnace, and have apertures in them for receiving the injection lances, allowing the jets from the lances to be directed toward the melts in the furnace.
In order for the gases and particulates from the lances to interact with the melt at the bottom of furnace, the portals in the walls of the furnace are located down near the melt. This means that the shields located in these portals are subjected to very high temperatures and highly corrosive or reductive environments. The shields protect the lances from the metal production environment of the furnace. The jets may even result in slag from the surface of the melt splashing up on the shields. When that happens, the slag may cool and collect on the shields.
The shields have different shapes and are made from different materials. Some shields are made from refractory material with apertures through them. Other shields are made from metal and water cooled. The water cooling function of shields utilizing water cooling is handled by many different configurations. Many water cooled shields rely on sets of complex passages which are difficult to manufacture and which may have locations of low fluid flow where heat is not adequately conducted away from the shield. Other shields are designed to accumulate a protective layer of slag from splash from the melt. However, those designs do not always conduct the heat away in a uniform manner and may develop hot spots in the features designed to accumulate the slag. Hot spots can lead to material altering temperatures at locations in the shield, with material failure being a possibility.
There remains a need for a shield that is simple in configuration and construction, and yet effectively conducts heat away from the surface exposed to heat, and that avoids hot spots in the exposed surface. Embodiments of the shield disclosed and claimed in the present application satisfy these needs.